Synthesis of hollow structured PtNi/Pt core/shell and Pt-only nanoparticles via galvanic displacement and selective etching for efficient oxygen reduction reaction

•Surface-morphology controlled PtNi nanoparticles were prepared by galvanic displacement and acid etching.•Pt-rich surface and hollow structure were formed by acid etching.•H-PtNi/Pt catalyst showed a superior ORR activity with improved durability.•Hollow PtNi/Pt core/shell structure plays an important role for enhancing ORR activity.